1. Field of the Invention
The invention relates in general to providing electrical power for radar modules and more specifically to decentralizing power distribution by providing dedicated power cells to the radar modules.
2. Discussion of the Related Art
Radar systems, such as Synthetic Aperture Radar (“SAR”) systems configured aboard satellites, are often supplied electrical power by a centralized power distribution system. For example, a satellite may be configured with a plurality of solar panels to generate electrical energy. Each of the solar panels, via individual photovoltaic cells or “solar cells”, receives and converts solar energy to electrical energy. The electrical energy is transferred to a centralized power distribution system which stores the electrical energy in batteries.
The centralized power distribution system transfers electrical energy from the batteries to various components aboard the satellite that require electrical energy to operate. An example of one such component includes a radar system. The radar may consume electrical energy to generate electromagnetic pulses towards a scene of interest. The radar may also consume electrical energy as reflected pulses are received by the radar. For example, the radar may include a receiver that receives reflected pulses and converts those pulses to digital data. This reception and conversion of the reflected pulses also consumes electrical energy.
To implement the functions of transmitting and receiving electromagnetic pulses, radars typically possess a plurality of sensitive electronic components configured as transmit/receive modules. For example, some radars, such as SARs, use a plurality of transmit/receive modules to transmit electromagnetic pulses. Each of these modules typically includes sensitive electronics that consume a significantly smaller fraction of the overall electrical energy stored with the centralized power distribution system (e.g., typically, low voltage current of about 3 to 4 volts Direct Current; “DC”). Although, a transmit/receive module typically consumes more electrical energy during transmission of electromagnetic pulses, the centralized power distribution system must manage and down convert stored electrical energy for operation of the sensitive electronics of such transmit/receive modules during all phases of operation (e.g., transmission, reception and digital conversion).
Power requirements for a radar system increase as more transmit/receive modules are added to the system. For example, a relatively large aperture phased array antenna radar system may require considerable amounts of power to function. Typical centralized power distribution systems for such phased array antennas collect energy through the solar panels which is subsequently transferred to a centralized voltage regulator and associated power conditioner. The voltage regulator and power conditioner provide power to a plurality of relatively large capacity batteries (e.g., 60 to 200 Amp-hour batteries) to charge the batteries. These batteries thereby supply power to a payload (e.g., a radar system) through a power distribution unit, typically at 28 volts. Power is subsequently distributed from the batteries to transmit/receive modules of the radar system via 28 volt-DC power lines and also to an antenna via a high-voltage bus to reduce power losses.
When distributing the power, a typical centralized power distribution system boosts voltage of a power signal supplied to reduce transmission loss. Boosting the power to higher voltages (e.g., 96 volt-DC or higher) typically requires an assembly of costly, complex, and heavy circuits. For example, a power boost regulator that boosts voltage from 28 volts-DC to 100 volts-DC may weigh over 190 kg. The main bus filter used in filtering ripple to the transmit/receive modules may also be relatively heavy (e.g., weighing over 23 kg), as well as having a relatively large volume (e.g., about 43 cm×31 cm×23 cm).
Additionally, power losses are inherent to the cumulative inefficiencies associated with power transfer from solar collection to distribution to the transmit/receive modules. For example, when power is subsequently delivered to a transmit/receive module, the power is converted through the use of a voltage de-boost circuit. Voltages at the transmit/receive modules may “droop” to significantly lower levels through such a voltage de-boost circuit. A droop as used herein generally refers to a change from a higher voltage to a lower voltage but not necessarily confined to an undervoltage condition. Accordingly, when multiple transmit/receive modules are employed, larger power management burdens are placed upon the centralized power distribution system. These management burdens often result in complex, expensive, and relatively heavy equipment.
Phased array radar antennas may employ hundreds of thousands of transmit/receive modules. For example, the number of transmit/receive modules associated with a SAR corresponds to resolution; more transmit/receive modules typically means better SAR image resolution. It is common for large phased array radars to draw in excess of 20 kilowatts DC peak power (i.e., high voltage and/or high current). Each transmit/receive module, however, draws a significantly smaller portion of the total power as such transmit/receive modules operate at low voltages of about 3.5 volts-DC. Since power must be distributed in high voltage (e.g., between about 96 volts-DC and 120 volts-DC) to reduce transmission loss, voltages delivered to each transmit/receive module must be down converted to the 3.5 volts-DC of the transmit/receive modules.
Such down conversion results in complex equipment because scaling from substantially high voltages to relatively small voltages is not easily done. For example, power distribution to the individual transmit/receive modules typically must be well behaved and regulated within ±5% of nominal (e.g., 6 volts-DC or 0.05×120 volts-DC). To achieve ±1% regulation at the transmit/receive modules, additional filtering is required during the voltage conversion from high voltage. Such is provided by DC-DC converters, which also supply negative reference voltage for the transmit/receive modules but add to the complexity of the system. Power distribution is further complicated because transmission lines from a centralized power distribution system must be strung throughout the entire array to transfer power to each transmit/receive module. For example, transmission lines must be tediously connected to each of the transmit/receive modules which may number in the hundreds of thousands. The transmission lines also add to the overall mass and size of the space vehicle.